@article{DM_2001_13_1_a7,
     author = {V. A. Vedernikov and D. G. Koptyukh},
     title = {Compositional formations of $c$-length~3},
     journal = {Diskretnaya Matematika},
     pages = {119--131},
     year = {2001},
     volume = {13},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DM_2001_13_1_a7/}
}